Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic systems. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), phase change memory (PCM) and Flash memory.
Non-volatile memory is memory that can retain its stored data for some extended period without the application of power. Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices are commonly used in electronic systems, such as personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones, and removable memory modules, and the uses for Flash memory continue to expand.
Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage of the cells, through programming of a charge storage structure, such as floating gates or trapping layers or other physical phenomena, determine the data state of each cell. Flash memory devices typically require relatively large voltages for programming and erasing operations. For example, a Flash memory device may have a supply voltage (e.g., Vcc) of 3V but require a voltage (e.g., Vpgm) of 15V or higher to be used during programming and/or erase operations on the array of memory cells. However, a sense (e.g., read) operation of Flash memory might only require voltages of Vcc or less, for example.
PCM is a resistive memory technology that can provide non-volatile storage but has the potential of relatively faster operation compared to flash memory. PCM, as the name implies, uses the change in resistance of a material when it changes phase in order to store data in a non-volatile manner. For example, an alloy of different elements might change from a crystalline phase having a low resistance to an amorphous phase having a high resistance. If the material could exhibit multiple distinctly different resistances, each different resistance can then be assigned a respective data value (e.g., 00, 01, 10, 11).
The phase change in PCM is brought about by heating the phase change material of each memory cell when it is addressed. This can be accomplished by a heater for each memory cell. When the heater is enabled by a current, it heats a chalcogenide alloy (e.g., germanium, antimony and tellurium (GeSbTe) or GST). When GST is heated to a relatively high temperature (e.g., over 600° C.), its chalcogenide crystallinity is lost. The GST cools into an amorphous glass-like state having a high electrical resistance. By heating the chalcogenide alloy to a temperature above its crystallization point but below the melting point it will transform back into a crystalline state having a lower electrical resistance.
The demand for higher operating speeds and greater storage capacity in memory devices continues to increase. This demand is accompanied by a need for a reduction in the latency of signals propagating within memory devices in order to facilitate the desired increase in operating speed. The latency of these signals can be cumulative and undesirable in light of the demand for reducing overall latency in memory devices. One source of latency in memory devices is circuitry (e.g., circuit(s)) which are commonly referred to as decoder circuits. These decoder circuits introduce delays (e.g., increase signal latency) as these signals propagate through one or more levels (e.g., layers) of decoder circuits in a memory device.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for decoder circuits which facilitate a reduction in the delay of signals propagating within memory devices.